port b62dbf1e (r30132).

original commit messge:

    Support for undetectable strings was officially dropped in
    https://codereview.chromium.org/916753002, but the compilers
    weren't fixed properly.

BUG=

Review URL: https://codereview.chromium.org/1287173002

Cr-Commit-Position: refs/heads/master@{#30156}